Aleppo (Syria) (AFP) – Western hesitation to support moderate rebels in Syria has strengthened the hand of jihadists among them, giving an increasingly Islamist tint to the rebellion against Bashar al-Assad, rebels in Aleppo say.

They spoke about what led 13 rebel groups, including theirs, to join Al-Qaeda-affiliated Al-Nusra Front Wednesday in rejecting the Western-backed National Coalition and its Syrian Military Council.

A joint statement said the Coalition "does not represent us, nor do we recognise it".

It also called on everyone fighting to topple the Syrian president to unite under a "clear Islamic context that... is based on sharia (Islamic law), making it the sole source of legislation".

That was an apparent reference to the jihadists' aspirations of creating an ultra-conservative Islamic state in Syria.

It has raised fears in the West about an increasing radicalisation of the rebellion and drew a sharp warning from Coalition chief Ahmad Jarba that extremists were trying to "steal our revolution".

The rebellion has always consisted of disparate groups, ranging from a handful of Western-style liberals to mostly moderate Muslims and, again, a small number of jihadists.

Earlier this month, defence consultancy IHS Jane's said the number of hardline Islamists among an estimated 100,000 rebels was nearly half the total.

'It was all lies'

A commander of one of the brigades in Aleppo's Old City placed the blame for the move squarely at US President Barack Obama's feet.

"The United States promised the people of Syria that it would not allow Assad to cross the red line and would attack, but it was all lies," said Abu Ammar, whose brigade is one of the most powerful rebel groups in Syria.

Abu Ammar was referring to Obama's threat to hit Syria over an August 21 chemical weapons attack that killed hundreds of people and that Washington blamed on Assad regime.

He claimed people in Aleppo "have no faith in the international community or the promises of the West, which has led them to ally with Islamists and groups linked to Al-Qaeda".

Part of the change in alliance is purely pragmatic, as it is the jihadists who have given punch to the war effort, says Abu Mohammed, a Sunni Muslim imam who acts as a sort of chaplain to the men of the Liwa al-Tawhid group.

"The United States and the West are... radicalising people. In the face of their indifference, we have begun aligning with Al-Qaeda, because it is they who are fighting and dying for us while the world just looks on."

Rebel fighters have always resented the fact that most of the opposition's political and military leadership lives abroad.

Abu Abeida, a commander of another brigade that signed the declaration, Shabab al-Daraa, said bluntly: "You can't talk about Syria from Turkey. We don't want to have anything to do with politicians who are not inside Syria fighting with us."

Jarba, who spoke at a meeting in New York of the Friends of Syria group, himself took a swipe at the West for its inaction.

Extremism "has increased because of the indifference of the international community, which has failed in its duties to the Syrian people", he said.

The opposition has repeatedly called for arms from its international backers, but the West has been reluctant to deliver for fear that weapons could fall into the hands of extremist groups such as Al-Nusra.

The change of allegiance is also increasingly ideological, these rebels in Aleppo say.

Abu Mohammed claims people have lost interest in creating a secular, democratic state, such as in neighbouring Turkey, and lean increasingly toward a state along Islamic models.

"We need an Islamic state, but not one based on radical Islamism. There are many countries that are religious and where religion is used as the basis of law, such as Saudi Arabia," he said.

There is even a belief among some people that the United States is playing a double game and that, despite its demands that Assad step down, it is actually supporting him.

"The Americans support all the dictators in the Middle East, and if it gets rid of any of them it is just to put a new one in his place," Abu Ammar said.